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(11) | EP 1 571 850 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Apparatus and method for encoding and decoding image containing grayscale alpha channel image |
| (57) An apparatus and a method for encoding and decoding an image containing a gray alpha
channel image are provided. The apparatus for encoding an image comprises: a block
data reception unit, which receives image data of a block currently being input to
the apparatus and classifies the current block either as a foreground image portion
or as a background image portion according to the values of gray alpha components
contained in the current block; a foreground image encoding unit, which sequentially
encodes the gray alpha components and brightness and hue components of the current
block if the current block is classified as the foreground image portion; and a background
image encoding unit, which encodes the gray alpha components of the current block
if the current block is classified as the background image portion. The apparatus
for decoding an image comprises: a bitstream interpretation unit, which interprets
the bitstream in units of predetermined blocks and classifies a current block obtained
as one of the interpretation results either as a foreground image portion or as a
background image portion; a foreground image decoding unit, which generates a restored
gray alpha channel image and a restored brightness and hue image by sequentially decoding
gray alpha components and brightness and hue components of the current block if the
current block is classified as the foreground image portion; and a background image
decoding unit, which generates a restored gray alpha channel image by decoding the
gray alpha components of the current block if the current block is classified as the
background image portion.
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